ARM: dreamplug: Enable FDT support

I have tested booting both FDT and non-FDT based Linux kernels (based on
http://marc.info/?l=linux-arm-kernel&m=133002679716986 and
http://marc.info/?l=linux-arm-kernel&m=132328894303581 respectively).

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Cc: Jason <jason@lakedaemon.net>
Cc: Prafulla Wadaskar <prafulla@marvell.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>

include/configs/dreamplug.h

@@ -148,4 +148,6 @@
  */
 #define CONFIG_DISPLAY_CPUINFO
 
+#define CONFIG_OF_LIBFDT
+
 #endif /* _CONFIG_DREAMPLUG_H */